Hydraulic servomotor mechanism for machine tools



Oct. 24, 1950 o. E. SCHURR 2,527,458

HYDRAULIC smvomo'roa MECHANISM FOR momma TOOLS Filed Dec. 21, 1945 2 Sheets-Sheet 2 INVEN TOR.

OTTO E SCHURR BY TOM'QTM AT TO R NEYS Patented Oct. 24, 1950 HYDRAUL IC SERVOMOTOR MECHANISM FOR MACHINE TOOLS Otto E. Schurr, Hamilton, Ohio,v assignor, by

mesne assignments, to Lima-Hamilton Corporation; Hamilton, Ohio, a corporation of Virginia Application December 21, 1945, Serial No. 636,390

18 Claims.

This invention pertains to a hydraulic circuit for machine tool. More particularly, this invention pertains to an improved hydraulic operating and control circuit for the relatively movable members of a machine tool.

One of the objects of this invention is to provide a hydraulic circuit for effecting the relative movement of the work andtool holders of a machine tool in a highly efficient and accurate manner.

Another object is to provide a hydraulic circuit for a machine tool which is controlled by power from the main drive motor of the machine tool.

It is also an object to provide, in a machine tool having a work spindle driven by a main drive motor, a hydraulic circuit for applying fluid pressure to actuate a tool holder relative to the work spindle, the hydraulic circuit being controlled in its rate of application of powergto the tool holder by power from the main drive motor.

A still further object is to provide a hydraulic circuit including servo valve mechanism for effecting a wide range of speeds for the relative movement of the work and tool holders of a machine tool.

It is also-an object to provide a simplified hydraulic servo valve circuit capable of effecting a broad range of feed and rapid traverse relative movements of the work and tool in a machine tool.

Further features and advantages of this invention will appear from a detailed description of the drawings in which:

Figure l is a diagram showing the application of this novel hydraulic circuit to a machine tool having relatively movable work and tool holding members.

Figure 2 is a diagram showing the application of the hydraulic circuit of Figure 1 to a machine tool having a plurality of movable members.

Referring to Figure 1, the novel hydraulic circuit is shown applied to a machine tool having a work holder 5 and a tool holder 6 movable relative thereto. In this particular illustration, the work holder 5 is of the rotary or work spindle type and is driven froma source of power or main drive motor I through a suitable mechanical power transmission indicated by the line 8. The tool holder 6 is actuated by a fluid pressure cylinder 9 having a piston l0 and piston rod ll appropriately connected to the tool slide or tool holder 6.

Power for actuating the fluid in the hydraulic circuit is derived from a suitable source of power or hydraulic pump motor l2 which is connected through a suitable drive connection and shaft l3 to a high pressure hydraulic pump 14 and a low pressure hydraulic pump [5. Each of these pumps receive a fluid supply through the respective suction lines I6 and II from the fluid reservoir l8.

It is also within the contemplation of this invention to drive the hydraulic pumps l4 and 15 directly from the main drive motor as indicated by the broken line arrow l9 which represents diagrammatically a suitable power transmission connected to the shaft |3a for driving-both of the pumps [4 and I5. In this respect, a separate hydraulic drive motor l2 would be dispensed with and there would ,then be provided an arrangement whereby the main drive motor directly actuated the work spindle 5 and also provided the power for energizing the hydraulic circuit for operating the tool holder 6.

The high pressure pump [4 at all times discharges'fluid pressure into the main pressure supply line 20. A branch line 20a-of this main supply line2ll is connected to a suitable pressure relief valve 2! which is in turn connected through the drain line 22 for return of discharged fluid from the valve 2! to the reservoir ill, the purpose of this valve being to limit the maximum pressure which may be developed in the line 20 to safe operating limits.

It will be noted that a single pressure supply line 20 is connected to the hydraulic servo control valve 23. A main discharge, return or drain line 24 is also connected to the valve for the return of fluid to the reservoir [8. Appropriate operating lines 25 and 26 are interconnected between the servo valve 23 and the operating cylinder 9 for the tool holder 6.

In the servo valve 23 is provided an axial reciprocatable control plunger 21 having appropriate grooves 27a aligned with the supply line 20 and drain'lines 24 so that movement of this valve plunger may reversibly control the direction and also the rate of flow of fluid to and from the cylinder 9. In conjunction with the valve 23, there is also provided an auxiliary seepage drain line 28 which is arranged to connect with the grooves 29 of the servo valve plunger so as to receive any leakage from each end of the valve plunger during the normal operation of the valve. This supplemental drain or seepage line 28, it is to be noted, is connected to the reservoir for return of seepage fluid independent of the normal main return line 24. In this way, the surge in the line 25 caused by maximum displacement of the servo valve plunger 21 during rapid traverse movement of tool holder 6 is not permitted to cause leakage to go past the ends of the valve plunger 21.

The servo valve plunger 21, when displaced slightly from its centralized or stop position for the cylinder 9, effects feeding movements with high fluid pressure in the tool holder 6. Under these conditions of feed movements the high pressure pump M transmits fluid at low volume and high pressure through the supply line 20 to the servo valve 23. The high pressure existing in the line 20 at this time is transmitted through a branch line 20b to the pressure chamber 36 of the bypass control valve 3I so as to raise its plunger 32 against the compression spring 33 connecting the chamber 34 with the chamber 35. This allows discharge from the low pressure pump I5 at a predetermined pressure, determined by the spring 33 opposing the pressure in the chamber 30, to pass through the lines 36 and 36a to enter the drain line 31 for return of fluid to the reservoir I8. Under normal feeding conditions the low pressure pump pressure supply is thus bypassed so that it merely circulates fluid from the line H to the line 36, through the valve 3| to the drain line 31.

Should it be desired to effect rapid traverse movements in the tool holder 6, the valve plunger 21 of the servo valve 23 is displaced a relatively large amount from its neutral or stop position. This provides a large discharge opening from the cylinder 9 to the main drain line 24 and correspondingly decreases the pressure required to move its piston I by pressure supplied by the line 26. Pressure thus dropsin the line 26 during rapid traverse movements which in turn, through the branch line 26b, decreases pressure in the pressure chamber 36 of the bypass valve 3'I. The

plunger 32 is thus forced downwardly by the greater pressure of the spring 33, closing discharge from the low pressure pump I through the lines 36 and 36a into the drain line 31. At the same time, the pressure drop in the line 20 decreases below the pressure in the line 36 as normally maintained by the spring 33 opposing the pressure in the chamber 30 acting on the plunger 32 so that the check valve 38 opens so that fluid pressure from the low pressure pump I5 passes through the line 36 and the line 36b through the check valve 33 into the branch line 200 of the main supply line 20. In this way, the low pressure pump I5 automatically supplements the flow provided by the high pressure pump I4 to provide an additional low pressure large volume supply in the line 20 to effect the desired rapid traverse movement in the tool holder 6. Thus it can be seen that the servo control valve 23 is arranged to be supplied by fluid pressure from a dual pump and that the single supply line connected to the servo valve is capable of providing any desired feed or rapid traverse movement for .the tool slide actuating cylinder by merely effecting the desired amount of displacement of the servo valve plunger.

The servo valve plunger 21 is preferably actuated by a servo valve screw 39 which is attached to the valve plunger 21 and arranged for axial movement to reciprocate the valve plunger but provided with any suitable means to maintain it in nonrotatable condition. Preferably, the servo valve 23 is mounted rigidly on the machine frame while an actuating nut 40 is journaled against axial displacement in a suitable bearing 4I fixed in the actuable member, tool slide, or tool holder 6. By rotating the nut 40 the screw 39 and the connected valve plunger 21 are moved relative to the valve 23 momentarily during the initial adjustment of the valve. The rotation of the nut 40 also re-adjusts the position of the valve plunger 21 and screw 39 relative to the'tool carrier 6 to in this way effect the relative servo control movement of tool slide as in a conventional manner for such servo valve mechanism.

The nut 40 may be rotated manually by means of a hand wheel 42 which is journaled for axial sliding movement on a suitable bearing 43 on the.

shaft 44. This shaft is journaled on bearings 45 preferably on the tool carrier 6. The shaft 44 is provided with a bevel gear 46 which in turn meshes with a mating bevel gear 41 on a shaft 48 which in turn has a bevel gear 49 adapted to enage a bevel gear 50 formed on the servo screw nut 46. The hand wheel is provided with clutch teeth 5I which are adapted to engage mating clutch teeth 52 on a clutch member 53 fixed to the shaft 44 by a pin 54. A compression spring 55 normally holds the hand wheel 42 in disengaged position of the clutch teeth 5I and 52. When the hand wheel 42 is pushed inwardly to engage these clutch teeth and rotated, the nut 46 may thus be relatively adjusted to move the screw 33 and valve plunger 21 relative to the tool slide 6 and valve 23 to effect the servo control.

Means are provided for automatically rendering the hand wheel ineffective to adjust the servo valve when the fluid pressure pumps I4 and I5 are not operating or the pressure in the hydraulic circuit has dropped below a predetermined safe operating level. A lockout plunger 56 is arranged to be moved between the clutch members 5| and 52 by a suitable compression spring 5'! when fluid pressure in the line 20 and branch line 20d drops below a predetermined safe operating level or drops to zero when the pumps I4 and I5 are not being driven. .Thus the hand wheel 42 cannot be moved inwardly to engage the clutch teeth 5| and 52 under these conditions. As soon as the pumps I4 and I5 are started so that proper operating pressure exists in the main line 20, pressure in the branch line 26d enters in the pressure chamber 58 behind the lockout plunger 56 to raise its piston 59 against the spring 51, thus withdrawing the plunger 56 and permitting engagement of the hand wheel clutch members 5I and 52. The purpose of this arrangement is to prevent re-adjusting the servo valve when the machine is shut down, particularly to a wide open position, and then energizing the hydraulic pump motor I2. This would cause a surge of pressure in the tool slide cylinder which in turn causes the tool slide to jump ahead and thereby move the servo valve beyond its other position and damage the valve or otherwise position the servo valve plunger in an inoperative location. Thus, with this arrangement, the tool slides and servo valves cannot be adjusted by the hand wheels so long as the hydraulic system is inoperative.

The servo screw nut 46 may also be reversibly driven by power received from the main drive motor and transmission indicated by the line 8 through a rate changer 60 including a suitable feed reverser which effects different rates of variable speed output through suitable transmission mechanism indicated by the line 6I which is connected to one member 62 of a feed and rapid traverse clutch. The other member of this clutch is connected to a reversible rapid traverse driving power source such as a rapid traverse electric motor 64 connected through a suitable transmission indicated by the line 65 to the member 63. The clutch member 63 may also, if desired, be driven by a connection indicated by the broken arrow 66 directly from the main drive motor and transmission 3, in which case the separate rapid traverse motor 64 would not be utilized, while a suitable reverser 66a is provided for reversing the rapid traverse drive.

A suitable clutch selector member 61 is this arrangement, the servo screw nut may be operated at variable feeding speeds by the rate changer 60 or at rapid traverse .rate, either from the independent electric rapid traverse motor 64 or from the main drive motor I through the drive connection 8-66-65.

In certain types of machine tools, it is desirable and essential to move the tool feeding device 6, having an integral lug it, up against a fixed abutment ll carried in the machine frame F so as to positively stop the tool slide in a predetermined accurate position. In a servo valve control mechanism which is power driven as above described, when the tool slide reaches and engages the fixed abutment, the servo valve plunger 27 and screw 39 continue to be adjusted in displaced position and thereby to further open the servo valve and apply additional fluid pressure to the operating cylinder'lli forthe tool It is therefore desirable to at some slides 6. point during this over-adjustment of the servo control valve after the tool slide engages the abutment, to automatically arrest furtheradjustment of the servo valve plunger. There has therefore been provided an automatic means to stop further adjustment of the servo valve after a predetermined amount of adjustment has taken place. in the servo valv plunger upon engagement of the tool slide with the fixed abutment.

As an example of a preferred arrangement to accomplish this result, there is provided a limit switch 12 carried on the machine frame F which is operatively electrically connected through suitable leads I3 and electrical apparatus with the magnetic clutch 69. On the servo screw 39 is fixed an actuating cam M having appropriate cam surfaces 15 and 16 which engage andoperate the control arm TI of the limit switch 12 when the relative adjustment of the screw 39 and servo plunger 21 exceeds a predetermined value either side of the neutral or stop position of the valve. Thus, as the tool slide engages the abutment H and its motion is thus definitely stopped, the servo screw continues to be adjusted by the power drive above described until the relative movement of the screw 39 causes either surface H5 or it to engage the limit switch 12. The magnetic clutch 69 is thus de-energized to automatically disconnect all power drive to the servo screw nut and bring the servo valve to a stop in an opened position.

In order to reverse or back the tool slide away from the flxedabutment, .theoperator engages ,the manualcontrol hand wheel 42 to connect the clutch members 59 and 52 and rotates the hand wheel in the reverse direction until the servo valve has been brought back toward the neutral or stop. position. As soon as the servo valve has thus been re-adjusted toward its neutral position,limit switch 12 is released and the maghydraulic circuit principles to a machine tool having a plurality of actuable members or tool slides or holders 6, Ba, 6b, and 6c, each appropriately mounted on the machine frame and .connected to be moved by the respective fluid pressure cylinders 9, 8a, 9b, and 90. Each of these cylinders is provided with appropriate pistons 90 and piston rods ii connected to the tool slides or holders 6 to 60 inclusive. Each of the cylinders 9 to 90 inclusive is controlled by appropriate servo valves 23, 23a, 23b, and 230 in the manner shown in Figure 1. The cylinders are each connected by suitable connecting lines 25 and 26, 25a and 26a, 25b and 26b, and 250 and 260, respectively to the servo valves 23 to 230 inclusive. Gravity balancing valves 25; are connected in lines 25a and 250 to oiTset the downward weight of the tool bars 6a and to by providing iree flow from the servo valves 23a and 23a to the bottom of the cylinders 9a and 90, but providing a restricted flow out of the bottom of these cylinders to balance the normal downward movement or the tool bars. This allows the same effective servo control for both up and down movements of the bars. Each of these servo valves may be controlled by power applied to the servo screws 39, 39a, 39b, and 39c through the respective nuts at, Mia, 40b, and we as in Figure 1. Manual control may be efiected by the hand wheels 42, 62a, 42b, and Me as in Figure 1.

In connection with slides 6 and 6b, the hand wheel actuating mechanism for adjusting the threaded rods connected with the servo valve members are carried by the slides so as to move therewith. In this manner the gearing connecting the hand wheels with the threaded rods is always engaged and the rods can be manually adjusted at any time that it is possible to engage the clutches associated with the hand wheels.

The hand wheel mechanism associated with the slides 6a and 60, on the other hand, are stationary as are the housings of the servo valves 23a and v23c. However, the spur gearing 49, 400 for servo valve 230 and 49, Mia of servo valve 23a permit a certain amount of reciprocation of the threaded valve adjusting rods relative to the hand Wheel structures. Inasmuch as the valves are normally maintained very close to their center position, the said threaded rods will at all times be drivingly engaged with the hand wheel mechanism and can be adjusted thereby at any time the clutches of the hand wheels can be engaged.

The source of fluid pressure in this arrangement is derived from a pair of dual tool pumps l4l5 and Mal5a. Each of these dual pumps I l-I5 and l4al5a is driven from a common source of power or electric motor l2a and receives a supply of fluid through the. suction lines 18. The dual pump I4--i5 transmits pressure through a single pressure supply line 19 which is connected to the servo valves 23 and 23a while the dual pump Ida-15a transmits pressure through another single pressure supply line to the servo valves 23!) and 230. This system is so arranged that one or the other or both of the dual Pu ps may be operated to supply pressure to the respective lines 19 and 80. This may be accomplished by providing by-pass valves '81 and '82 for connecting the discharge from the respective pumps back to the reservoir l8 when it is desired to cut out one or the other of these pumps when the motor Fla is energized- Thus, in this system some of the tool slides may be rendered 7 inoperative even though the hydraulic pump motor I 2a is energized.

It is to 'be further noted that individual lockout plungers 56 are provided for each of the hand wheel controls in a manner as shown in Figure l and appropriately connected to the corresponding pressure supply lines for the associated servo valve of each particular hand wheel. In other words. the hand wheels 42 and 42a are provided with the lockout plungers 56 and 58a, these lookout plungers being operatively hydraulically connected by suitable lines 19a with the pressure supply line 19 from the dual pump M-ii. The

hand wheels Mb and 420 are provided with the lockout plungers 56b and 56c connected through the branch lines 80a with the pressure supply line 80 from the other dual pump I la-a. Thus each of the tool slides or carriers 6, 6b, 6a or 60 may be operated independently of one another with this hydraulic circuit arrangement with all of the various desired servo control functions for the group of tool slides rendered manually operative by the readily available handwheels 82, 42a, Mb, and Me.

It is to be further noted that this circuit is well adapted for use of auxiliary clamping mechanism for other machine members. For example, a clamping mechanism comprising a clamping cylinder 83 having actuable pistons 86 and piston rods 85 including a control valve 86 operable by a solenoid Blmay be utilized. This valve 86 is connected by a main pressure supply line 88 through a pair of check valves 89 and 90 to the respective pressure supply lines 19 and 80 from each of the dual pumps. A suitable re- 1 turn line 9! is connected to the reservoir l8 for the return of fluid from the clamping cylinder 83. The check valves 89 and 90 provide means so that either one or both of the dual pumps may be operated while at all times allowing the full manipulation of the clamping mechanism indicated by the cylinder 83.

Each of the servo control valves is connected to a main drain or return line 9|, as in Figure 1, for the return of fluid to the reservoir i8, and it is to be noted that each of the actuating cylinders for the tool slides is provided with bleeder lines 92 having air bleeder choke coils 92a connected through an independent circuit indicated generally at 92 for return of seepage and bleeder discharge from the cylinders and servo valves to the fluid reservoir or to the main drain line at a point remote from the connection of the main drain line with the servo valves.

While the apparatus herein disclosed and described constitutes a preferred form of the invention, it is to be understood that the apparatus is capable of mechanical alteration without 'departing from the spirit of the invention and that such mechanical arrangements and commercial adaptations as fall within the scope of the appcndant claims are intended to be included herein.

Having thus fully set forth and described this invention, what is claimed as new and desired to be secured by United States Letters Patent is:

1. In a hydraulic servomotor mechanism for relatively'movable members of a machine tool, a hydraulic pump, a drive motor for said pump connected to directly mechanically actuate one of said members, a hydraulic motor to actuate the other member, a hydraulic circuit interconnecting said pump and hydraulic motor for actuating the othermember, a servo valve in said circuit actuable in opposite directions from a neutral position to reversibly vary the rate of flow in said circuit and the rate and direction of operation of said hydraulic motor, and means for reversibly actuating said servo valve in control functions by power derived from said driving motor for said pump and one member, said lastmentioned means including means for varying the rate of application of power from said drive motor to said servo valve, and means operable automatically upon movement of said servo valve a predetermined distance in either direction from its neutral position for interrupting the application of power thereto from said drive motor.

2. In a hydraulic servomotor mechanism for a machine tool having a relatively movable work holder and a tool holder, a main drive motor for actuating one of said holders, a hydraulic motor connected to actuate the other holder, a fluid pressure pump, a hydraulic servo valve interconnecting said pump and motor, drive means including a connection to said main drive motor for selectively driving said servo valve relative to said other holder at a plurality of different speeds to cause said motor to effect movement of said other holder at diflerent speeds, and control means automatically operable by the engagement of said other holder with a fixed abutment to disconnect said drive means from said servo valve, said means comprising an electrical control switch operable by the relative position of adjustment of said servo valve, and electrical means responsive to the operation of said switch to tie-energize a magnetic clutch interconnecting said drive means with said servo valve.

3. In a hydraulic servomotor mechanism for a. machine tool having a work holder, a main drive electric motor for actuating said work holder, 2. tool holder movable relative to said work holder, a hydraulic motor for actuating said tool holder, and a positive stop for limiting the movement of said tool holder at a predetermined position relative to said work holder, the combination of a servo control valve for regulating the application of fluid pressure to said motor, means for connecting power from said main drive motor to actuate said servo valve to effect feed and rapid traverse movements in said tool holder, an electrically operable connect and disconnect means between said main drive motor and said servo valve, and electrical control means for said electrically operable means actuated by the adjustment of said servo control valve to a predetermined position after engagement of said tool holder with said positive stop to automatically disconnect power from said main drive motor to said servo valve.

4. In a hydraulic servomotor mechanism for actuating a machine member including, a hydraulic cylinder and a plunger reciprocable therein, a servo control valve hydraulically connected to said cylinder, and a source of fluid pressure connected by a single supply line to said servo valve, the combination of a high pressure fluid pump and a low pressure fluid pump, means for driving said pumps, a fluid reservoir for both of said pumps, a discharge line from said high pressure pump to said single supply line for said servo valve, a bypass valve controlled by pressure from said high pressure pump to cause said low pressure pump to discharge into said reservoir, and means in connection with said bypass valve responsive to the pressure drop in said single supply line caused by the adjustment ofsaid servo control valve for automatically directing the supply from said low pressure pump into said single supply-line to said servo valve in addition to the constant supply provided by said high" pressure pump for any adjustment of said servo valve to effect rapid traverse rates of movementioi said machine member, manual control means for ad-* justing said servo valve, and means responsive to a predetermined pressure in, said sin'gle'supply line below the pressure supplied by either of said pumps to render said manual controlmeans ineffective to adjust said servo valve.

said element with said connections to receive power from said-drive motor.

9.111 a hydraulic servomotor mechanism for a machine tool having relatively movable work and tool holders, and a drive motor for one of said holders; a fluid motor for actuating the other holder, a source of fluid pressure and a servo valve connecting said source of pressure with said fluid motor and having a valve member 5. In a hydraulic servomotor mechanism for a movable work holder and tool holder, a main I drive power means for directly actuating one of said holders, a fluid motor for actuating the other holder, a fluid pressure pump, a hydraulicseryo valve interconnecting said-pump with said fluid j; motor to actuate said other holder, means for adjusting said servo valve comprising high and low speed drives driven from said-'main ;drive motor, and a clutch having one position wherein the high speed drive is effective and another posi-J tion wherein the low speed drive is. efi'etiv. f

6. In a hydraulic servomotor mechanism ariav machine tool having relatively movable work and.

movable in opposite directions from a neutral position to determine opposite directions of movement of said other holder, a connection from said valve member to said other holder including an element movable for adjusting said connection, a drive from said drive motor to said element including a normally engaged clutch, and means responsive to a predetermined amount of movement of said valve member in either direction from its neutral position for effecting disengagement of said clutch.

'7. In a hydraulic servomotor mechanism for a machine tool having relatively movable work and tool holders, and a drive motor for one of said holders; a fluid motor for actuating the other holder, a source of fluid pressure and a servo valve connecting said source of pressure with said fluid motor and having a valve member movable in opposite directions from a neutral position to determine opposite directions of movement of said other holder, a connection from said valve member to said other holder including an element movable for adjustingsaid connection, a plurality of driving connections from said drive motor for said element for adlusting said connection at different speeds, and a manually operable clutch for selectively connecting said element with'said connections to"' receive power from said drive motor,

movable in opposite directions from a neutral position to determine opposite directions of movement of said other holder, a connection from said valve member to said other holder including an element movable for adjusting said connection, a pluralityof driving connect ons. from said drive motor for said element for ad-' lusting said connection at different speeds, at least-one thereof being reversible, a manually operable clutch for selectively connecting said element with said connections to receive power from said drive motor, and other clutch means between said element and said manual clutch responsive to a predetermined amount of movement of said valve member in either direction from. its neutral position for effecting disengage ment of said other clutch means.

10. In a hydraulic servomotor mechanism for a I machine tool having relatively movable work and tool holders, and a drive motor for one of said, holders; a fluid motor for actuating the other holder, a source of fluid pressure and a servo valve connecting said source of pressure with said fluid motor and having a valve member movable in opposite directions from a neutral position to determine opposite directions of movement of said other holder, a connection from said valve member to said other holder including an element movable for adjusting said connection, a drive from said drive motor to said element including a normally engaged clutch, means responsive to a predetermined amount of movement of said valve member in either direction from its neutral position for eflecting disengagement of said clutch, and

5 manual drive means for said element -including a normally disengagedclutch, said manual drive following disengagement thereof.

11. In a hydraulic servomotor mechanism for a machine tool having a work holder and a movable tool holder and a drive motor for the work holder; a fluid motor for actuating the tool 55 holder, a source of fluid pressure and a servo --motorandincluding a valvemember movable in opposite directions from a neutral position to 8; In a hydraulic servomotor mechanisiffor determine. opposite directions of movement oi.

a machine tool having relatively movable work and tool holders, and a drive motor for one of said holders; a fluid motor for; actuating the other holder, a source of fluid pressure and a servo valve connecting said source of pressure with said fluid motor and having a valve member movable in opposite directions from a neutral position to determine opposite directionsof movement of said other holder, a connection from said valve member to said other holder insaid tool holder, a nut rotatably mounted on said tool holder and a threaded rod therein con-:-

nected with said valve member, driving connection means from said drive motor to said nut including a normally engaged clutch, and means 55 responsive to a predetermined amount of movement of said valve'member in either direction from its neutral position for eflecting disengagement of said clutch.

12. In a hydraulic servomotor mechanism for a machine tool having a work holder and a movable tool holder and a drive motor for the work holder; a fluid motor for actuating the tool holder, a source of fluid pressure and a servo valve connecting said source with said fluid motor and including a valve member movable in opposite directions from a neutral position to determine opposite directions of movement of said tool holder, a nut rotatably mounted on said tool holder and a threaded rod therein connected with said valve member, driving connection means from said drive motor to said nut including a normally engaged clutch adjacent said nut, and speed changing and reversing means adjacent said drive motor.

13. In a'hydraulic servomotor mechanism for a machine tool having a work holder and a movable tool holder and a drive motor for the work holder; a fluid motor for actuating the tool holder, a source of fluid pressure and a servo valve connecting said source with said fluid motor and including a valve member movable in opposite directions from a neutral position to determine opposite directions of movement of said tool holder, a nut rotatably mounted on said tool holder and a threaded rod therein connected with said valve member, driving connection means from said drive motor to said nut including a normally engaged clutch, means responsive to a predetermined amount of movement of said valve member in either direction from its neutral position for effecting disengagement of said clutch, a manual drive means connected with said nut and including a second and normally disengaged clutch, a member for locking said second clutch in disengaged position and normally urged toward its locking position, and means responsive to a predetermined minimum pressure at the inlet of said valve for moving said locking member out of its locking position.

14. In a hydraulic servomotor mechanism for a machine tool having a work holder and a movable tool holder and a drive motor for the work holder; a fluid motor for actuating the tool holder, a source of fluid pressure and a servo valve connecting said source with said flu d motor and including a valve member movable in opposite directions from a neutral position to determine opposite directions of movement of said tool holder, a nut rotatably mounted on said tool holder and a threaded rod therein connected with said valve, driving connection means from said drive motor to said nut including a normally engaged clutch, means responsive to a predetermined amount of movement of said a valve member in either direction from its neutral position for efiecting disengagement of said clutch, and a manual drive means connected with said nut and includin a second and normally disengaged clutch, and means for mantor and including a valve member movable in opposite directions from a neutral position to determine opposite directions of movement of said tool holder, a nut rotatably supported by said tool holder and a threaded rod therein connected with said'valve member, a drivin connection from said drive motor to said nut ineluding a normally energized electromagnetic clutch, a switch in series with said clutch and actuatable for de-energizing said clutch, and cam means on said rod positioned so movement of said rod and valve member a predetermined distance either direction from the neutral position of said valve member will bring said cam means into actuating engagement with said switch.

16. In a hydraulic servomotor mechanism for a machine tool having a rotary work spindle and a movable tool holder and a drive motor for said spindle; a fluid motor for actuatin said tool holder, a source of fluid pressure and a servo valve connecting said source with said fluid motor and including a.valve member movable in opposite directions from a neutral position to determine opposite directions of movement of said tool holder, a nut rotatably supported by said tool holder and a threaded rod therein connected with said valve member, a driving connection from said drive motor to said nut including a normally energized electromagnetic clutch, a switch in series with said clutch and actuatable for de-energizing said clutch, cam means on said rod positioned so movement of said rod and valve member a predetermined distance either direction from the neutral position of said valve member will bring said cam means into actuatin engagement with said switch, and manual means for driving said nut when said clutch is de-energized.

1'7. In a hydraulic servomotor mechanism including a fluid motor, a source of fluid pressure and a servo valve connecting said source with said motor and having a movable valve member, manual means for moving said valve member and including. a normally disengaged clutch manually engageable, a locking member for locking said clutch in its disengaged position, and means responsive to a predetermined fluid pressure for moving said locking member to ineffective position and hydraulically connected with the inlet of said servo valve to be acted on by the pressure therein.

18. In a hydraulic servomotor mechanism including a fluid motor, a source of fluid pressure and a servo valve connecting said source with said motor and having a movable valve member, manual means for movin said valve member and including a normally disengaged clutch manually engageable, a locking member for lockin said clutch in its disengaged position, a spring urgin said locking member toward effective position, and fluid operable means arranged to oppose said spring and hydraulically connected with the inlet of said servo valve whereby actuation of said valve member by said manual means is possible only when there is a predetermined pressure at the inlet of said servo valve.

O'I'IO E. SCHU'RR.

REFERENCES strap The following references are of record in the file of this patent:

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